It is important to save power in a 1-to-N communication system in which one base unit communicates with a plurality of handsets.
Patent Document 1 discloses a security communication apparatus that saves power with a simple configuration in which each handset performs transmission at the timing set in advance for each handset, and the base unit identifies each handset based on the time lags between the transmission timings of handsets.
Patent Document 2 discloses a wireless system where a handset saves power by performing carrier sensing when an applicable timing comes to the handset in 1-to-N intermittent reception and by stopping carrier sensing when timings come to other handsets.
Now, device use limiting apparatuses that disable the use of a device itself such as a mobile telephone when the device is left or stolen and carried away from the hands of the owner or user, and gives a warning that the device is more than a predetermined distance away, are becoming popular.
FIG. 1 illustrates a use limiting method for limiting the use of a mobile terminal apparatus using wireless authentication communication.
As shown in FIG. 1, when mobile terminal apparatus 10 such as a mobile telephone is carried away from the hands of user 1 and goes out of the authentication distance, the use of mobile terminal apparatus 10 is disabled and wireless communication unit (hereinafter “key unit”) 20 owned by user 1 sounds an alarm to warn that mobile terminal apparatus 10 is left. To be more specific, in a system where wireless authentication is performed by receiving radio signals between key unit 20 and the use delimiting unit of mobile terminal apparatus 10, when each unit detects that a received level goes below a predetermined value, the use of mobile terminal apparatus 10 is limited by stopping transmission of use delimiting signals from the use delimiting unit, and key unit 20 outputs a warning signal. By this means, it is possible to prevent a mobile terminal apparatus from being left or stolen.
FIG. 2 is a block diagram in which a use limiting method of the mobile terminal apparatus of FIG. 1 is implemented.
FIG. 2 shows: mobile terminal apparatus 10 such as a mobile telephone/PHS (Personal Handy-Phone System), PDA (Personal Digital Assistants), notebook PC, MP3 player and HDD player; and key unit 20 that, when the distance is spaced more than a predetermined distance apart, automatically locks mobile terminal apparatus 10 and sounds an alarm by communicating (i.e. polling) with mobile terminal apparatus 10. Mobile terminal apparatus 10 and key unit 20 have wireless authentication sections 11 and 21, respectively, for performing wireless authentication with each other. Key unit 20 is driven by battery 22.
Wireless authentication section 21 of key unit 20 and wireless authentication section 11 of mobile terminal apparatus 10 perform authentication utilizing wireless communication. Wireless authentication section 21 of key unit 20 and wireless authentication section 11 of mobile terminal apparatus 10 have ID's associated in advance, and perform authentication at all times by learning by means of wireless communication that these ID's are the pair.
FIG. 3 shows the basic operations of wireless authentication between mobile terminal apparatus 10 and key unit 20.
As shown in FIG. 3, key unit 20 transmits search signals on a regular basis using a search channel during a search. Mobile terminal apparatus 10 that receives this search signal cross-checks the ID of mobile terminal apparatus 10 and the ID of key unit 20 included in the search signal, and returns a response signal if the ID's form a pair that is registered in advance. Key unit 20 also cross-checks the ID of the mobile terminal apparatus included in the response signal and the ID of key unit 20. After the above initial authentication is finished, authentication starts using an authentication channel. During authentication, authentication is performed by sending data encrypting random numbers (i.e. authentication signal 1), from mobile terminal apparatus 10, and sending data decoding the random numbers (i.e. authentication signal 1′), from key unit 20.
While mobile terminal apparatus 10 and key unit 20 authenticate each other, it is possible to operate mobile terminal apparatus 10 without any problem. In case where authentication is not performed adequately, the operation of mobile terminal apparatus 10 is limited and key unit 20 sounds an alarm.
FIG. 4 shows a use limiting system formed with one key unit and a plurality of mobile terminal apparatuses. As shown in FIG. 4, a plurality of mobile terminal apparatuses that perform wireless authentication with key unit 20 are terminal A of a mobile telephone, terminal B of a digital camera and terminal C of a mobile printer. Key unit 20 and these terminals A to C form a use limiting system and perform 1-to-N communication. Although FIG. 4 shows an example of a combination with three mobile terminal apparatuses, combinations with a greater number of mobile terminal apparatuses such as PDA's and notebook PC's are possible.
FIG. 5 shows the operations of wireless authentication between key unit 20 and terminals A to C of FIG. 4. As shown in FIG. 5, key unit 20 performs 1-to-1 communication with terminals A to C. For example, when terminal A transmits an authentication request to key unit 20, key unit 20 returns an authentication response to terminal A. Similarly, when terminal B transmits an authentication request to key unit 20, key unit 20 returns an authentication response to terminal B and, when terminal C transmits an authentication request to key unit 20, key unit 20 returns an authentication response to terminal C. In this way, 1-to-N communication in the use limiting system combines the operations of 1-to-1 wireless authentication of FIG. 3 corresponding to the number of mobile terminal apparatuses.    Patent Document 1: Japanese Patent Application Laid-Open No. 2001-209874    Patent Document 2: Japanese Patent Application Laid-Open No. 2003-217067